This invention relates to silicon wafer fabrication and in particular, to methods for limiting the formation of stacking faults in oxidized silicon wafers.
Typically silicon wafers to be oxidized are first degreased and subjected to a wet chemical cleaning consisting of a scrub and HCl--H.sub.2 O.sub.2 and NH.sub.4 OH--H.sub.2 O.sub.2 boils in order to remove impurities from the wafers which can result in stacking faults after oxidation. Even with careful cleaning and handling such as is discussed above, many times there is an undesirable density of stacking faults formed after oxidation.
The article entitled "Elimination of Stacking Faults in Silicon Wafers by HCl added Dry O.sub.2 Oxidation" at pages 747-751 of the Japanese Journal of Applied Physics Vol. 14, No. 6, June 1975, teaches the adding of small amounts of HCl during dry oxidation to decrease stacking faults. The method taught requires temperatures generally in excess of 1200 degrees C and is not useful at lower temperatures. This method also requires relatively a long period of time to be effective and is impractical in many cases because it would result in too much oxide being formed and because many partially fabricated silicon wafers can not be heated to the temperature at which the method is effective. In addition, in this method the surface stacking fault nucleation sites, such as impurities, are not eliminated during oxidation. Furthermore, the method is not applicable to wet or steam oxidations.
It would be desirable to limit surface induced stacking faults in silicon wafer by eliminating the surface nucleation sites (e.g., impurities) with a short duration cleaning process performed prior to oxidation and effectively carried out at temperatures compatible with processing of the wafers.